1. Field of the Invention
The present invention is directed toward a zoom optical system for optical instruments such as microscopes, and particularly a zoom optical system in which the conjugate lengths of the lens assemblies may be adjusted.
2. Description of the Prior Art
In the past, zoom optical systems have been widely incorporated into optical instruments, such as microscopes. Generally, in such zoom optical systems a pair of lens assemblies are connected by way of cams or linkages to a zoom focus knob. As the knob is rotated, the zoom lens assemblies are moved with respect to each other by the cams/linkages so that a predetermined zoom magnification ratio is achieved. However, the positional relationship of the individual zoom lens assemblies with respect to each other, as well as the other fixed lenses in the instrument, is critical. Any error in this relationship will result in an unacceptable image quality. The result will be a rejected instrument until the error has been corrected. It is evident that highly precise parts must be incorporated in the initial design for the zoom optical system to function as designed.
Additionally, as the position of the zoom lens assemblies is fixed by design, there can be no error allowed in the assembly of the instrument. Very precise assembly techniques are required. The precision required in manufacturing parts, in addition to the degree of accuracy dictated during assembly add substantially to the cost of the instrument.
The optical system of the present invention provides a zooming mechanism which is simple, yet quite accurate and offers the additional feature of being adjustable to allow post-assembly modifications to accommodate for varying conjugate lengths of zoom lens assemblies to be easily and readily accomplished.